Modern rapid distribution systems for fresh meats rely upon refrigeration and plant sanitation to provide a wholesome product to the consumer. Although fresh meats in the United States are generally safe and free of hazardous levels of pathogens, the microbial quality may be poor; high levels of non-pathogenic spoilage bacteria, frequently present, dramatically shorten shelf-life and affect the taste and appearance of the meat. In response to this problem, several states and the Federal Government have adopted or proposed standards regulating the bacterial content of fresh meat.
It is recognized that refrigeration is not a complete solution to spoilage problems because the principal spoilage bacteria are psychrotrophs which grow well at 5.degree.-15.degree. C., or mesotrophs which are adapted to grow at lower temperatures. Ayres, J. C. (Food Research, 25:1, 1960) found that the dominant microorganisms growing on refrigerated beef comprised the Micrococci and Pseudomonads; even at temperatures as high as 15.degree. C. the growing bacterial population was dominated by motile gram negative rods of the Pseudomonas generae. Other bacteria commonly present of fresh meat include the gram negative, flagellated generae: Serratia, Aeromonas, Proteus, etc. Together with the Pseudomonads, these are responsible for off-color and slime production in decaying meat. Mesotrophs, typically the food-borne pathogens such as Salmonella, E. coli and gram positive anaerobes such as Clostridia, are now believed to be "free riders" and, particularly at refrigerated temperatures, do not grow appreciably on meat surfaces; despite their dangerous nature they have no substantial role in food spoilage. (For example, see Goepfert, J. M., J. Milk Food Technol., 38:449, 1975).
Bacterial contamination of retail meat has been the subject of extensive studies whose conclusions are here set forth. The microorganisms present in retail portions are derived directly from the initial bacterial load on the carcass surface immediately post-slaughter; thus, meat portions, such as hamburger, having high bacterial counts are traceable to carcasses having high surface contamination. (For example, see Elliot, et al., Applied Microbiology, 9:452, 1961). The primary source of such contamination is the gut and hide of the animal itself, although the packing house environment (floors, chill room, cutting room, etc.), and handling by packing house workers are all substantial sources of contamination. (Frazier, Food Microbiology, Chapt. 16, 2d ed., 1967) Prolonged storage, as in aging, also increases contamination from the air, etc. Subsequent handling, as in transit, cutting, boning and packing, may offer serious contaminating events.
Several available processes eliminate bacteria from meat by killing them with a contact disinfectant(s) applied in the form of a spray to the carcass surface during chilling. U.S. Pat. No. 3,745,026 (Hansen) discloses such a process utilizing 50-200 ppm of aqueous chlorine (hypochlorous acid). U.S. Pat. No. 4,021,585 (Svoboda, et al.) describes an alternative process utilizing 5-50 ppm of aqueous chlorine dioxide. Both processes achieve reduced bacterial counts during the chill cycle (18-24 hrs. post-slaughter) by killing bacteria introduced onto the carcass during slaughter procedures. This is shown by the reduction in viable colony-forming bacteria present at the end of the chill cycle as compared with counts at the beginning of such period after carcasses are conveyed to the chill room from the kill floor.
A major problem with such use of chlorinated contact disinfectants is reaction of the agent with meat components to produce chloro-organic derivatives such as chloro-substituted lipids and chloro-aromatic compounds. These chlorinated derivates pose a potential health hazard, especially the class of halomethanes (known to be carcinogenic) formed by reaction of bactericidal levels of hypochlorous acid with humic or other organic substances. Reaction of chlorine dioxide at bactericidal concentrations with meat components results in lower but detectable levels of organic chlorine.
Other agents such as inorganic and organic acids have also been applied to carcass surfaces in the form of aqueous sprays, as described in Carpenter, J. A., Proc. Meat Indust. Res. Conf., Chicago, 1972. Use of these agents has not received widespread acceptane because of substantial surface damage to the carcass, and the off-odors and flavors imparted to the meat at bacteriostatic concentrations.